Maarg Manthan · Topic 10.10

Factors Responsible for Soil Formation and Soil-Forming Processes

Environment & Ecology › Land, Forest and Soil Resources · Topic 10.10

Soil formation is controlled by five factors, summarised by Hans Jenny as climate, organisms, relief, parent material and time. Parent material sets the mineral composition and texture; climate, through rainfall and temperature, drives weathering, leaching and microbial activity; relief or topography affects drainage, erosion and depth; organisms such as plants, microbes and earthworms add organic matter and mix soil; and time allows horizons to develop. Several processes then shape soils: laterisation in hot, wet climates, where heavy leaching removes silica and leaves iron and aluminium oxides; podzolisation in cool, humid coniferous forest regions, giving acidic soil with a bleached layer; calcification in semi-arid regions, where calcium carbonate collects in the subsoil; salinisation in dry areas with high evaporation; gleization under waterlogging; and humification, eluviation and illuviation, which move organic matter and minerals within the profile.

5 min read · UPSC Prelims · Environment & Ecology · Land, Forest and Soil Resources

At a Glance

Factors Five (CLORPT)
Hot wet process Laterisation
Cool humid process Podzolisation
Dry process Calcification
Waterlogging Gleization
Exam link UPSC Prelims, Environment & Ecology: Land, Forest and Soil Resources

Where Does It Fit?

This topic follows the basics of soil characteristics and explains what controls them. It leads to soil profiles and horizons, which show the results of these processes. Previous topic: Soil Characteristics and Soil Formation Process. Next topic: Soil Profiles and Horizons.

Which Factors Control Soil Formation?

Factor	Role
Parent material	Rock or sediment that supplies minerals and decides texture, for example basalt gives black soil and granite gives sandy or red soil
Climate	Rainfall and temperature decide weathering, leaching, organic matter decay and soil type; the most active factor
Relief (topography)	Slope controls drainage and erosion; steep slopes have thin soils, valleys have deep, wet soils
Organisms	Vegetation, microbes, earthworms and termites add humus, mix soil and cycle nutrients
Time	Soils need long periods to form horizons, so young soils like alluvium are less developed
Human activity	Farming, irrigation, drainage and erosion modify soil quickly
Jenny’s equation	Soil is a function of climate, organisms, relief, parent material and time

Which Soil-Forming Processes Matter?

Laterisation: hot, humid regions with alternate wet and dry seasons; heavy leaching of silica leaves iron and aluminium oxides, giving red or laterite soils
Podzolisation: cool, humid regions under coniferous forest; acidic litter leaches iron and aluminium and forms an ash-coloured layer
Calcification: semi-arid and arid grasslands; low rain lets calcium carbonate build up in lower layers
Salinisation: dry, flat areas where evaporation exceeds rain, so salts rise to the surface
Gleization: waterlogged soils lacking oxygen, with blue-grey colours
Humification: breakdown of litter to humus
Eluviation: washing out of material from upper layers
Illuviation: deposition of that material in lower layers

What Else Should You Remember?

Jenny: Hans Jenny, a Swiss-American soil scientist, set out the five factor model in 1941
Active and passive factors: climate and organisms are active factors, while parent material, relief and time are passive
Granite parent: produces sandy to loamy acid soils
Basalt parent: produces fine, clay-rich black soil in the Deccan
Limestone parent: produces calcium-rich soil
Alluvium: river-deposited sediment, young soil
Loess: wind-blown silt that forms fertile soil
Rainfall effect: heavy rain leaches nutrients, while low rain leaves salts
Temperature effect: warm conditions speed up chemical weathering and microbial action
Slope effect: soil creeps and erodes on steep slopes, and gathers at the base
Aspect: sun-facing slopes are drier and warmer than shaded slopes
Vegetation: forests give acidic litter, grasslands give thick dark humus
Chernozem: very fertile dark grassland soil of temperate steppes formed by calcification and humification
Podzol: acidic forest soil of cold climates in the taiga, with poor fertility
Laterite: hard red soil in tropical monsoon uplands that bakes hard when dry
Terra rossa: reddish soil on limestone in Mediterranean climates
Saline soil: white salt crust on the surface in dry regions
Bioturbation: mixing of soil by animals and roots
Soil age: old soils are highly weathered and nutrient poor, as in parts of the tropics
Man-made changes: terraces, irrigation and fertiliser change soil over decades
Link to previous: see Soil Characteristics and Soil Formation Process
Link to next: see Soil Profiles and Horizons
Link to soil types: see Types of Soils in India and the World
Caution: most real soils form through several processes at once, so labels are simplifications
Exam hint: match each process with its climate and the typical soil
Climate zones and soils: tropical humid zones give laterites and oxisols, temperate grasslands give chernozems and prairie soils, and cold forests give podzols
Role of vegetation cover: dense roots bind soil and litter feeds humus, while bare land loses soil faster than it forms
Man as a factor: some soil scientists add human activity as a sixth factor because ploughing, irrigation and fertiliser change soils quickly
Decalcification: leaching of lime from the upper layers in humid areas
Soil formation rate varies: warm, wet climates weather rock faster than cold or dry ones
Local relief and drainage: flat low land holds water and favours gleization, while slopes drain and erode

Why Does It Matter for the Exam?

Factors: Five
Hot wet process: Laterisation
Cool coniferous: Podzolisation
Current affairs link: Soil carbon and health
Common errors: mixing laterisation with podzolisation or calling time an active factor

As an analytical point, climate and vegetation work together to decide how a soil develops, so shifting rainfall patterns and land use change will gradually change soils. Understanding the process helps predict where erosion or salinity will hit.

Why Is This Topic Important?

Factors Five
Hot wet Laterisation
Dry Calcification

What Came Next?

The next topic covers soil profiles and horizons. Next topic: Soil Profiles and Horizons.

Key People and Terms

Laterisation Leaching in hot wet climate
Podzolisation Acid leaching under conifers
Calcification Lime build-up in dry zones
Gleization Waterlogged soil process
Eluviation Washing out
Illuviation Washing in

Exam Corner

Points to Remember

Five factors: CLORPT.
Laterite: hot and wet.
Podzol: cool conifer.
Calcification: semi-arid.
Gley: waterlogged.

Do Not Confuse With

Eluviation and illuviation Removal versus deposition
Laterisation and podzolisation Hot humid versus cool humid
Active and passive factors Climate and life versus rock, relief, time

Memory Hook

Climate, life, slope, rock and time make soil, process picks the kind.

Mains Angle

Questions ask for factors and processes. These points help.

Factors Five
Processes Climate linked
Use Prediction

A Question You May Face

An original practice question, not a past paper question.

“Explain the factors that control soil formation and describe the major soil-forming processes.”

How to Answer

Factors CLORPT.
Processes Climate linked.
Examples Soils.
Use Management.

GS Relevance

Prelims: factors and processes, matching with climates. GS Paper 1: soil geography.

Frequently Asked Questions

What are the factors of soil formation?

The five factors of soil formation are parent material, climate, relief or topography, organisms and time, as set out by Hans Jenny. Parent material gives the minerals, climate drives weathering and leaching, relief controls drainage and erosion, organisms add humus and mix the soil, and time lets horizons develop.

Which factor is most important in soil formation?

Climate is generally treated as the most important factor because rainfall and temperature control weathering, leaching, biological activity and vegetation. Together with organisms it is an active factor, while parent material, relief and time are passive factors that provide material, setting and duration for the process.

What is laterisation?

Laterisation is a soil-forming process in hot, humid tropical regions with alternate wet and dry seasons, where heavy rain leaches silica and bases from the soil. Iron and aluminium oxides remain, giving a reddish, hardening soil called laterite that is low in nutrients, common in the Western Ghats, Kerala and the north-east.

What is podzolisation?

Podzolisation occurs in cool, humid regions under coniferous forests, where acidic litter makes water acidic and leaches iron and aluminium from the upper layers. This forms a pale ash-coloured layer and an accumulation layer below, leaving a poor, acidic soil called podzol, common in the taiga.

What is the difference between eluviation and illuviation?

Eluviation is the removal of material, such as clay, iron and organic matter, from an upper soil layer by water moving downward. Illuviation is the deposition of this material in a lower layer. Together they produce the distinct horizons, with a leached upper layer and an enriched subsoil.

PYQ Practice — Statement Analysis

1 Soil formation depends on five main factors.

True

Parent material, climate, relief, organisms, time.

2 Laterisation occurs in cold dry climates.

False

In hot humid climates.

3 Calcification occurs in semi-arid regions.